Although prostate cancer is a major medical problem, the current methods of medical imaging are only marginally successful in differentiating cancerous prostate tissue from normal tissue. Biopsies are typically performed with random sampling of tissue throughout the prostate. Imaging methods utilizing near-infrared radiation have the power to generate pictures with unprecedented contrast between cancerous and normal or benign tissue. However, the resolution of pure optical imaging is relatively poor. Optoacoustic tomography gives images with the contrast of an optical image but the resolution of ultrasonic imaging. It has already been shown to be highly successful in showing cancerous tumors in the human breast. The goals of this proposal are as follows: (1) To test the feasibility of a rectal optoacoustic probe containing both a light emitting-component and an array of ultrasonic transducers for detection of light-generated acoustic signals. (2) To develop a prototype unified rectal probe for prostate imaging. (3) To test the power of the probe to detect prostate cancer.